There is more than one way they could be connected, but there is no "typical" system. It depends on what the customer requested, or the plumber felt was the best way. You could have two independent systems, or one heater could be feeding its hot water into the other one.

: We recently purchased a second home which was built in 1978. The house is about 2700 square feet, and has 2 40 gallon gas hot water heaters.

: One heater is located in the garage. The first floor of the house has a kitchen w/dishwasher, laundry room, 3/4 bath with shower and a half bath (powder room).

: The second heater is located upstairs, where there are two bedrooms, the master bathroom has two sinks, shower and separate tub. Second bedroom bathroom has sink and shower.

: Here are my questions. How is a system like this typically plumbed? At first I assumed the upstairs heater fed the upstairs, and the garage heater fed the downstairs. However I noticed one day when I had the garage heater gas valve turned to low, I was getting hot water at the kitchen sink.

: I have never had a house with two water heaters, so any insight would be helpful. Is there a way of determining how this setup is plumbed? Only reason I ask; I was considering a "tankless" gas unit, since the house is vacant often. If I did this however, do I still need to plumb with two tankless units at the current locations? Appreciate any input/comments to understanding how two units work in a household.